The application relates to x-ray systems and methods and more particularly to x-ray based bone densitometry systems and methods and techniques useful at least in such systems and methods.
X-rays or gamma-rays can be used to measure the density and distribution of bone in the human body in order to help health professionals assess and evaluate projected bone mineral density, which in turn can be used to monitor age-related bone loss that can be associated with diseases such as osteoporosis. Additionally or alternatively, similar procedures can be used to measure non-bone related body content such as body fat and muscle. In bone densitometry, a patient typically is placed on a table such that the patient's spine extends along the length of the table, along a direction that can be called the Y-axis in Cartesian coordinates. For a supine patient, the left and right sides are in a direction typically called the X-axis. A source at one side of the patient transmits radiation through the patient to a radiation detector at the other side. The source and the detector typically are mechanically linked by a structure such as a C-arm to ensure their alignment along a source-detector axis which is transverse (typically perpendicular) to the Y-axis. Both x-ray tubes and isotopes have been used as a source of the radiation. In each case, the radiation from the source is collimated to a specific beam shape prior to reaching the patient to thereby restrict the field of x-ray or gamma radiation to the predetermined region of the patient opposite which are located the detectors. In the case of using x-rays, various beam shapes have been used in practice including fan beam, pencil beam and cone or pyramid beam shapes. When a fan beam is used, typically the beam conforms to a beam plane which is transverse (e.g., normal) to the Y-axis. Stated differently, the beam is wide in the plane and thin along the Y-axis. The shape of the beam and the shape of the detector system correspond. The detector in a fan beam system typically is an elongated array of detector elements arranged along a line or an arc. By means of mechanically moving the C-arm and/or moving the table, a region of interest in a patient on the table can be scanned with the radiation. Typical regions of analysis in bone densitometry include the spine, hip, forearm, and wrist, scanned individually. They can be covered individually within a reasonable time by a fan beam that has a relatively narrow angle in a single pass or, alternatively, by a pencil beam scanning a raster pattern. Another analysis region is termed "oblique hip" in which the hip is viewed at an angle relative to the horizontal and vertical directions. Another analysis region is referred to as "whole body" in which the entire patient body is scanned and analyzed for bone density and possibly also for "body composition" or the percentages of fat and muscle in the body.
X-ray bone densitometry systems have been made by the owner of this application under the tradenames QDR-2000+, QDR-2000, QDR-1500, QDR-1000plus, and QDR-1000. The following commonly owned U.S. patents pertain to such systems and are hereby incorporated by reference herein: U.S. Pat. Nos. 4,811,373, 4,947,414, 4,953,189, 5,040,199, 5,044,002; 5,054,048, 5,067,144, 5,070,519, 5,132,995 and 5,148,455; and 4,986,273 and 5,165,410 (each assigned on its face to Medical & Scientific Enterprises, Inc. but now commonly owned). Other bone densitometry systems are believed to have been made by the Lunar Corporation of Madison, Wis. (see, e.g., the system which is believed to be offered under the tradename Expert and U.S. Pat. Nos. 5,228,068, 5,287,546 and 5,305,368, none of which is admitted to be prior art against this application). It is believed that other manufacturers also have offered bone densitometry products.
The inventions disclosed in this application are directed toward bone densitometry features which are believed to overcome various shortcomings of such prior art systems. In a particular exemplary and non-limiting embodiment, the inventions are included in an x-ray bone densitometry system comprising a patient table having a length extending along a Y-axis and a width extending along an X-axis, a C-arm supporting an x-ray source at one side and an x-ray detector at an opposite side of said table, the source and detector being aligned along a source detector axis which is transverse to the Y-axis. When selectively energized, the source emits a fan beam of x-rays which conforms to a beam plane which is transverse to the Y-axis and contains the source-detector axis. At least one of said C-arm and table is selectively movable relative to the other along the X-axis, along the Y-axis, and along a Z-axis which is transverse to both the X-axis and the Y-axis, to selectively scan selected regions of a patient on the table with said fan beam of x-rays. In addition, the C-arm is selectively rotatable around a rotational axis extending along the Y-axis to selectively change the angle of the fan beam with respect to a patient on the table.
A beam modulator is mounted between the x-ray source and the table for rotation about a beam modulator axis which is transverse to the source-detector axis. The beam modulator is selectively rotatable about the beam modulator axis to cause the fan beam of x-rays to pass through a succession of beam modulating materials before reaching a patient on the table. These beam modulating materials having respective different effects on the x-rays impinging thereon, to modulate the beam for desired patient procedures and to serve other purposes such as to provide reference and calibration information.
An attenuator selector also is mounted between the x-ray source and the table and has a plurality of attenuating materials selectively movable to cause the fan beam to pass therethrough. Each of these attenuating materials attenuates the fan beam passing therethrough in a selected manner different from that of other attenuating materials to cause a desired change in beam parameters such as intensity, uniformity and energy spectrum.
A variable aperture collimator also is mounted between the x-ray source and the table to define the cross-section of the fan beam. The collimator can define the shape and size of the fan beam by passing x-rays through a selected one of several different slits in an x-ray opaque plate or, alternatively, can use a pair of plates selectively movable along the Y-axis to define one of the cross-sectional dimensions of the fan beam and a pair of plates movable along a direction transverse to both the Y-axis and the source-detector axis to define another cross-sectional dimension of the fan beam. A number of detector elements can be used to form said detector and to provide respective detector outputs related to the x-rays received at respective angular positions within the fan beam.
A detector response flattener can be used which is responsive to the detector outputs to process the outputs to account for at least one of: (i) non-uniformities in the fan beam; and (ii) non-uniformities in the response of detector elements. A dark current system can be used for interleaving the detector outputs with dark current responses of the detector elements on a substantially continuous basis, so as to use a dark current corrector which is responsive to the detector outputs and the dark current responses to account for dark current characteristics of the detector elements. An optical crosshair device can be mounted on the C-arm to project a visible crosshair co-axial with the source-detector axis and having a plane along the Y-axis and a plane normal to the Y-axis.
The scan motion controller can move at least one of the C-arm and the table relative to the other to scan at least a first region and then a second region of a patient on the table with the fan beam along the Y-axis, wherein the first region and said second region are next to each other along the X-axis, each region has an edge overlapping an adjacent edge of the other region, and the distance along the Z-axis from an origin of the fan beam in the source to the table remains the same for the scan of each of the first and second regions. The system can use a merger responsive to outputs of the detector for scans of the first and second regions to merge detector outputs for positions of the fan beam which are spatially adjacent along the X-axis but are obtained at different times, into resulting merged detector outputs corresponding to detector outputs obtainable from a single fan beam having substantially twice the width of the fan beam emitted from the source. A source controller selectively pulses the source to emit therefrom single energy and dual energy x-rays in time-interleaved manner, and a processor is responsive to detector outputs for these single and dual energy x-rays to derive from them diagnostic information based solely on single energy x-rays as well as diagnostic information based on dual energy x-rays.
A display coupled with the processor displays concurrently both the diagnostic information based on single energy x-rays and the diagnostic information based on dual energy x-rays. The scan motion controller moves at least one of the C-arm and the table relative to the other to carry out first a posterior/anterior or an anterior/posterior scan and then a lateral scan of a patient on the table without moving the patient between the two views. The scan motion controller rotates the C-arm around its rotation axis between carrying out the two scans, and selects the position of the source relative to the table for the lateral scan based on information respecting the patient's spine obtained in the course of the anterior/posterior or posterior/anterior scan. The scan motion controller stores scan sequences each corresponding to scanning a selected region of interest, or a selected set of regions of interest, in a patient on the table. An interface responsive to operator input selects a stored scan sequence, and the scan motion controller in response carries out the operator-selected scan sequence.
A patient positioner is removably supported on the table and has: (i) a base for supporting the head and upper shoulders of a patient who is supine on the table; and (ii) a pair of wings spaced from each other along the X-axis and extending up from the base for supporting the patient's arms when the patient's hands are under the patient's head and the elbows are to the left and right of, and elevated from, the patient's torso. The patient positioner is shaped and dimensioned to maintain the patient's arms and hands away from the patient's chest and to straighten the patient's spine. A forearm positioner also can be removably supported on the table at a selected distance along the X-axis from an edge of the table. The forearm positioner comprises a base with an opening therein corresponding to a position for a patient's wrist when the patient's forearm extends along the Y-axis and is held against the table, and further comprises a fence against which the patient's forearm can be pressed to limit movement of the patient's forearm along the X-axis in a direction away from said edge of the table.
The scan motion controller maintains the C-arm and the table at a selected relative position along the Y-axis while causing other relative motion between the C-arm and the table to obtain dual energy detector outputs for different relative positions between the C-arm and table while a patient is on the table. The system for such scanning can process the dual energy detector outputs to substantially cancel out soft tissue information while retaining bone information in the detector outputs, and can perform a computerized tomography image reconstructing bone structure but not soft tissue structure for which detector outputs have been obtained.
One "whole body" scanning technique described in this and the parent applications involves scanning the body in directions parallel to the Y-axis in successive passes which are spaced from each other in a direction parallel to the X-axis. The effect is similar to that of assembling a wider fan beam of x-rays from successive passes with narrower fan beams. While the simplified analysis of the narrow fan beam assembly into a wider fan beam may suggest that the centerline of the narrower fan is rotated about the focal spot hypothetical point of origin F (hereafter referred to occasionally herein for brevity as the "focal spot") between successive passes, this is not the case in the actual practice of this whole body scanning technique. In fact, the focal spot hypothetical point of origin moves in space between successive passes, along an arc centered at the center of rotation of the C-arm which carries the x-ray source and the x-ray detectors and the patient table also moves in directions parallel to each of the X-axis and the Z-axis between successive passes. In addition, in the preferred embodiment, the angular spacing between the centerlines of the narrower beams is often not the same as the beam width, to cause an effective overlap between the margins of successive beam positions.
A currently preferred "whole body" technique adds a different principle--a selective displacement of the narrower fan between passes to make the x-ray imaging magnification factor significantly different as between successive passes of the narrow fan of x-rays in a direction parallel to the Y-axis. Advantageously, this selective greater magnification is at the spinal region or the left and right hip regions of a supine patient centered on the patient table, whichever magnification is desired for a particular medical diagnostic test.